ALPS'17 Naoya Hirota

ALPS11-2 (invited) "Broadband ultrafast nonlinear photonics in nanocarbons

The presentation was on a mode-locked fiber laser utilizing the saturable absorption property of single-walled carbon nanotubes (SWCNTs). The image of the saturable absorption device used is shown in Figure 1, which closely resembles the device fabricated by Nakamura Lab. of the University of Tokyo, in which CNTs are synthesized on a fiber with a shaved surface. The fabrication process is spin-coating ⇒ CNT growth by CVD, and the CNT growth process is similar to the process of growing CNTs on toroids conducted at Maki Lab. What attracted my attention in this presentation was the measurement method of absorption properties. As shown in the experimental setup in Fig. 2, the input to the saturable absorption device is through a fiber, and the absorption property by coupling of evanescent light and CNTs can be measured without constructing a spatial system that is difficult to align, such as the Z-scan method that I had assumed. Therefore, it is expected that even the Tanabe Laboratory can easily perform the measurement once the device is fabricated. Figure 3 shows the results of absorption property measurements with different polarization, and it can be seen that there is a large polarization dependence in the absorption property of CNTs. This means that the SA of CNTs can be tuned widely by simply changing the polarization, and by utilizing the tuning range, CW light, mode-locked pulses, Q-switched pulses, and Q-switched mode-locked pulses were generated with a single device.